Update dotnet version

Author: AlexSatsukevich

.github/workflows/nuget-publish.yml

@@ -11,6 +11,6 @@ jobs:
       - uses: actions/checkout@v2
       - uses: actions/setup-dotnet@v1
         with:
-          dotnet-version: '3.1.x'
+          dotnet-version: '6.0.x'
       - run: dotnet pack src/Regula.DocumentReader.WebClient -c Release -p:PackageVersion=${{github.event.release.name}}
       - run: dotnet nuget push src/Regula.DocumentReader.WebClient/bin/Release/Regula.DocumentReader.WebClient.${{github.event.release.name}}.nupkg -k ${{secrets.NUGET_AUTH_TOKEN}} -s https://api.nuget.org/v3/index.json

.github/workflows/run-smoke-test.yml

@@ -15,7 +15,7 @@ jobs:
       - uses: actions/checkout@v2
       - uses: actions/setup-dotnet@v1
         with:
-          dotnet-version: '3.1.x'
+          dotnet-version: '6.0.x'
       - run: dotnet build src/Regula.DocumentReader.NetCoreExample -c Release
       - working-directory: src/Regula.DocumentReader.NetCoreExample/bin/Release/netcoreapp3.1/
         run: ./Regula.DocumentReader.NetCoreExample